1. Field of the Invention
The present invention relates to a cast iron or aluminum sectional boiler, in particular a condensing boiler.
2. Description of Related Art
Sectional boilers of this type are made up of a plurality of boiler sections cast in one piece which are situated one behind the other and connected to one another by hubs on the water side. Flow takes place through the water channels and water pockets formed by the boiler sections between the return connection and the feed connection. Sectional boilers according to the definition of the species generally have a lower return connection and a feed connection situated at the top, preferably in the particular hub. The heating gases overflow from the furnace chamber via downstream heating gas passages to a flue spigot and transmit heat to the boiler water on their way.
In all previous boilers of this type, the sections are situated in series one behind the other. There is an annular front section to which a furnace chamber door or a burner plate may be attached, one or more similarly designed center sections depending on the magnitude of the output, and a rear section. The furnace chamber extends through front and center sections to the rear section, which with its cover-like design, forms the floor of the furnace chamber. In these specific embodiments, all boiler sections have similar outside dimensions because they form parts of the furnace chamber, the heating gas passages and the water compartment across the entire boiler cross section. Furthermore, boilers for low output ranges which are made up of only two or even only one boiler section are also known.
With respect to the flue gas routing and the efficiency of the heating units, a distinction is made between thermal power technology and condensing boiler technology. More and more condensing boiler devices are being used for reasons of saving energy. The design of their heat exchanger allows for the possibility of cooling down the moist flue gases arising in operation during the combustion of fuel and air to below the flue gas dew point. During this process, the moisture of the flue gases is condensed out and in addition to the perceptible heat, the heat of condensation is transferred to the hot water.
When used as a condensing boiler, special attention must be given to the selection of materials, as the flue gases are contaminated due to the composition of the fuel used and due to the combustion process, and the accumulating condensation water contains various acids at a low concentration. The components in contact with condensation water such as heating surfaces, flue gas collectors, and the flue gas must thus be resistant to the acids, which is why these components are usually produced from stainless steel, aluminum, or plastic. Welded stainless steel heat exchangers are generally used, especially in oil condensing boiler technology, as is described, for example, as a helically wound pipe in published German patent application document DE 10 2004 023 711 B3. They offer the advantage of standing up to the high level of acidity without corrosion. Disadvantages are the high costs associated with the material as well as the less favorable scaling conditions in particular in welded sheet metal constructions and the larger physical sizes which make assembly difficult in confined spaces.
The heat exchangers of conventional thermal power boilers are frequently manufactured from cast iron. They are distinguished by high robustness and long life. Being assembled from mostly identical cast segments, they allow cost-effective production and easy scalability with respect to different magnitudes of output and offer good assembly possibilities even in confined installation conditions. The material stands up very well to brief flue gas condensation phases when operation is started and the heat exchanger is cold. In its present form and design, the only area where cast iron is not suitable is in a condensing boiler operation with extended accumulation of condensation water.
Furthermore, a condensing boiler having a compact heat exchanger made of corrosion-resistant material, which is integrated and connected downstream hydraulically, is known from published German utility model application document DE 296 21 817 U1. As a separate component, this compact heat exchanger is surrounded by two bowl-shaped boiler sections and connected separately on the water side. All boilers having a downstream heat exchanger have the disadvantages that the assembly expense is increased by the necessary pipe components and resistance on the water side rises. As a separate, external component, the system also causes cooling losses which must be reduced by suitable thermal insulation.